This invention relates to the spectral analysis of a scene, and, more particularly, to an instrument that can form and analyze the spectral radiances at each pixel of an image, in real time for continuous motion.
The objects in a scene are characterized by their spatial forms and their spectral radiances. The spectral radiance of an object is its reflected light intensity as a function of wavelength, and is indicative of the material which forms the object. Although the human eye can distinguish forms very well, it does not discern spectral radiance characteristics nearly as precisely. Instead, the human eye perceives only a dominant portion of the spectral radiance, which is perceived as the color of the object.
Since the spectral radiance of an object is a characteristic of that object, in principle most objects can be identified by their spectral radiances alone. However, because the human eye is a relatively unsophisticated observer of spectral radiances, it is not always possible to distinguish objects based upon their perceived colors. For example, at a distance a field of green corn cannot be readily distinguished from a field of green grass simply by their colors. On the other hand, the corn and the grass are readily distinguished from each other on the basis of their different spectral radiances, if the complete spectral radiances can be used in the analysis.
The spectroradiometer is an instrument that analyzes the spectral radiance of objects in its field of view. Existing spectroradiometers are designed to view only a single region at a time to obtain a pure spectral radiance of that region. An entire scene can be analyzed using the same approach in conjunction with one of several scanning techniques that steps the analysis region over the entire field of view. Such scanning spectroradiometers are relatively slow in operation. In particular, they cannot operate at the minimum rate of about 20-30 frames per second required to view a scene in what the eye perceives as continuous motion. Additionally, available spectroradiometers have limited usefulness in the infrared and X-ray portions of the spectrum.
There is therefore a need for high-speed imaging spectroradiometers that can perform spectral analysis on a pixel-by-pixel basis of entire scenes at rates of at least about 20 frames per second, and are useful in the infrared and X-ray spectra. Such spectroradiometers could be used in many applications such as medical diagnostics, earth resources, and resource management. The present invention fulfills this need, and further provides related advantages.